Purpose:
To investigate whether baseline visual field (VF) damage is a predictor of faster rates of progression in the Low-pressure Glaucoma Treatment Study (LoGTS).

Methods:
In this prospective, randomized, double-masked, multicenter clinical trial, patients with ≥5 VF tests during follow-up were included. To minimize a "floor effect" expected in eyes with severe VF loss on rates of VF change, only eyes with baseline MD better than -16 dB were included. Also, PSD is known to have an increasing monotonic function up to that MD cut-off value on average, which mitigates the effect of diffuse sensitivity loss on PSD values normally see after that point. Progression was determined using pointwise linear regression analysis, defined as the same 3 or more VF locations with a slope more negative than -1.0 dB/year at P <5%, on 3 consecutive examinations. Cox Proportional hazards method using a backward elimination approach was used to test whether known risk factors (age, IOP, central corneal thickness, treatment for systemic hypertension, migraine, Reynaud’s, and mean arterial ocular perfusion pressure) in addition to baseline mean deviation (MD) or pattern standard deviation (PSD) were associated with faster progression. Eyes with high PSD values at baseline were considered to have localized, deep VF loss, as opposed to diffuse loss when the MD was more negative.

Results:
Timolol and brimonidine groups had similar baseline MD (P=0.67) and PSD (P=0.84). In the multivariable model that included baseline PSD, randomization to timolol (Hazard Ratio, HR=3.27, P=0.001), older age (HR=1.03, P=0.014), treatment for systemic hypertension (HR=3.13, P=0.001), increased mean ocular perfusion pressure (HR=0.82, P<0.001), and worse PSD (HR=1.09, P=0.039). The model including MD did not reveal statistical significance of this variable (P=0.79). The average sensitivity of the 4 central-most points at baseline was a significant predictor of faster progression (P<0.001).

Conclusions:
In treated patients with low-pressure glaucoma, eyes with localized, deep, and central VF defects at baseline progressed faster than those with diffuse loss.